The present invention relates to a method for controlling a damper of a vehicle; and, more particularly, to a method for adjusting a damping force of the damper based on a steering status of the vehicle to thereby improve steering stability.
In general, a suspension system is installed at a vehicle to improve ride comfort and roadholding efficiency of the vehicle. The suspension system includes a spring and a shock absorber, i.e., a damper.
Conventionally, the damper is installed in parallel to the spring between a vehicle body and driving wheels of the vehicle. The damper absorbs vibrations of the vehicle that are caused by an impact on the spring at a time when the vehicle travels. By such an operation of the damper, the ride comfort is greatly improved.
The damper operates to reduce vertical kinetic energy and two kinds of dampers are conventionally used; one is a friction damper and the other is an oil damper.
The friction damper uses a frictional resistance. More specifically, the friction damper is operated by the frictional resistance generated between a damper case and a shaft while a coil spring continues to extend and contract. Due to the frictional resistance, the magnitudes of the extensions and contractions of the spring are gradually reduced and finally stopped.
The oil damper, on the other hand, uses viscous oil hermetically contained in the damper case. At the end of the shaft to be inserted into the damper case is prepared a piston. While the spring continuously extends and contracts, the piston in the oil moves up and down. Since the damper oil exhibits a viscosity hundreds times stronger than that of water, movements of the piston generate a considerable amount of resistance. Accordingly, the extensions and the contractions of the spring are gradually stopped.
In recent days, in the meanwhile, an increasing number of vehicles use a damper capable of controlling a damping force thereof to improve the ride comfort. The damping force is controlled by a control logic.
A conventional control logic controls damping force characteristics of the vehicle in relation to vehicle behaviors such as a ride, an anti-roll, an anti-dive, an anti-squat and a speed sensitive, etc.
However, since such a control logic is designed to be applied to a road in a high myu condition having a high frictional coefficient (xcexc), the control logic cannot cope with a spin phenomenon that occurs frequently on a road surface in a low myu condition with a low frictional coefficient (xcexc), i.e., a road surface in a slippery status, e.g., on an icy road or a road covered with snow. Moreover, the control logic may not effectively deal with an over-steer or an under-steer, either, that occurs frequently when a vehicle operator makes an abrupt steering action.
It is, therefore, an object of the present invention to provide a method for controlling a damper of a vehicle, wherein front and rear damping force of the damper is properly adjusted based on a steering status of the vehicle, thereby improving steering stability.
In accordance with a preferred embodiment of the present invention, there is provided a method for controlling a damper of a vehicle, said vehicle including a front damper and a rear damper, a damping force of said dampers being controlled by respective data detected by a steering angle sensor, a vehicle speed sensor and a yaw rate sensor, said method including the steps of:
(a) sensing steering angle data, vehicle speed data and yaw rate data;
(b) calculating a desired yaw rate by using the steering angle data, the vehicle speed data and a specification of the vehicle;
(c) comparing the desired yaw rate with the yaw rate data provided from the yaw rate sensor;
(d) determining whether the vehicle is over-steered or under-steered depending on the comparison result obtained in the step (c); and
(e) controlling the damping force of the damper in response to the determination result in the step (d).
In accordance with another embodiment of the present invention, there is provided a method for controlling a damper of a vehicle, said vehicle including a front damper and a rear damper; a damping force of said dampers being controlled by respective data detected by a steering angle sensor, a yaw rate sensor, a lateral G sensor, a wheel speed sensor and a vehicle speed sensor, said method including the steps of:
(a) sensing steering angle data, yaw rate data, lateral G data, wheel speed data and vehicle speed data;
(b) calculating a desired yaw rate by using the steering angle data and the vehicle speed data;
(c) comparing the desired yaw rate with the yaw rate data provided from the yaw rate sensor;
(d) determining whether the vehicle is over-steered or under-steered depending on the comparison result obtained in the step (c); and
(e) deciding whether a road surface is in a slippery state or not by using the vehicle speed data, the lateral G data and a specification of the vehicle such as a tread.
(f) controlling the damping force of the damper in response to the determination results made in the steps (d) and (e).